The State Emergency Service, SES, had conducted two flood rescues on Thursday night, one in Wollongong and one in Broken Hill, a spokeswoman said.

She said SES workers were also at Bargo assisting with the clean up.

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Mrs Briggs said a friend had been dining at the Bargo pub when an awning, which she said was about 30 metres long, was blown off the pub and onto the nearby railway line.

"Lucky nobody was killed," Mrs Briggs said.

She and her husband had been scooping rain water away from the back of their house with buckets to prevent it entering the home, she said.

A small gas main had also been damaged in Bargo when a large tree was struck by lightning, a spokesman for the Jemena gas company said. Local firefighters had switched off the gas and supply was not affected, he said.

The Transport Management Centre has advised the Southern Highlands railway line between Picton and Moss Vale has been partially closed by a fallen power pole and debris on the tracks around Bargo.

A limited bus service has replaced the trains.

The Bureau of Meteorology said the storms were part of a southerly change coming through the region and moving to the north-east.

"The line of storms extends all the way back into the hills in the back of Sydney," senior forecaster Jane Golding said.

"[There is] a lot of lightning and some very heavy rainfall," she said.

Ms Golding said the area just west of Wollongong received 100 millimetres of rain over just one hour.

Severe weather warning over

The Bureau of Meteorology published this update at 2.36am

"Severe thunderstorms are no longer occurring in NSW and the ACT. The immediate threat of severe thunderstorms has passed, but the situation will continue to be monitored and further warnings will be issued if necessary."